Do not forget the stick centering & ESC calibration ( you have to do it only once)
The manual says to start with low gain for first flight , but then it goes in any direction; try to start with gyro at +/-65% and back down until it is ok for you.

This video has been made by KapteinKUK, which is the creator of the KK board.
Pots are for G, gain.

He is talking about 'I-gain' and 'P-gain' (?) in his video for a quad.

I am setting up a tricopter. My Eagle board has one (!) MEMS gyro to control 'Pitch', Roll' and 'Yaw'.
Therefore there are 3 pots on the board to set the gain for 'Pitch', Roll' and 'Yaw'.
Same on a KKmulticontroller v.5.5 "Blackboard": 3 pots, to change the gain for Pitch, Roll and Yaw.

Can someone please explain, what does he mean, if he is talking about I-gain and P-gain

Those oscillations mean the gain is set too high on your gyro. So, in the first video, the oscillations on the roll axis, means you need to turn down your roll gyro's gain.

In the second video, the drift to the left, could be stick centering, but that really is the same as trims. You will have to apply trims to get it to remain somewhat level.

Remember, with a gyro only control board, all the board does is "resist rotation." That doesn't mean it will hold the copter level to the ground. It will try to maintain whatever orientation it is in, until you give it commands from the radio to roll. It's up to you controlling the radio to tell it where to remain level with the ground so to speak.

So, if your radio isn't trimmed, and its telling it to roll to the left, it's going to roll to the left and keep rolling as long as your radio is giving a roll left command. It's very important to get your radio trimmed properly for stable/steady flight.

wkm1 wrote "the KK board and the EAGLE N6 has only those 3 controls."
KK board informations are easily avalaible, it's not the case with Eagle N6.
However, it is highly probable that PID gains are also included in N6 firmware.